class ListNode{
    public int val;
    public ListNode prev;
    public ListNode next;

    public ListNode(int val){
        this.val = val;
    }
}

public class MyLinkedList {
    public ListNode head;//指向双链表的头节点
    public ListNode last;//指向双链表的尾巴节点

    //打印链表
    public void display(){
        ListNode cur = this.head;
        while(cur != null){
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();
    }
    //得到单链表的长度
    public int size(){
        ListNode cur = this.head;
        int count = 0;
        while (cur !=null){
            count++;
            cur = cur.next;
        }
        return count;
    }

    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        ListNode cur = this.head;
        while (cur != null){
            if(cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);//创建一个新节点
        if(this.head != null){
            node.next = this.head;
            head.prev = node;
            this.head = node;
        }else{
            this.head = node;
            this.last = node;
        }
    }
    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(this.head != null){
           this.last.next = node;
            node.prev = this.last;
            this.last = node;
        }else{
            this.head = node;
            this.last = node;
        }

    }
    //任意位置插入,第一个数据节点为0号下标
    public ListNode searchIndex(int index){
        //知晓cur的位置，即是要在哪里插入节点的位置
        ListNode cur = this.head;
        while (index != 0 ){
            cur = cur.next;
            index--;
        }
        return cur;//此时cur已经走到要插入的节点
    }

    public void addIndex(int index, int data) {
        ListNode node = new ListNode(data);
        if(index > size() || index < 0){
            System.out.println("位置不合法");
            return;
        }
        if(index == 0){
            addFirst(data);
            return;
        }
        if(index == size()){
            addLast(data);
            return;
        }
        ListNode cur = searchIndex(index);
        node.next = cur.prev.next;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;

    }

    //删除第一次出现关键字为key的节点
    public void remove(int key){
        ListNode cur = this.head;
        while(cur != null){
            if(cur.val == key) {
                if (cur == head) {
                    head = head.next;
                    //预防只有一个节点的情况
                    if(head != null) {
                        head.prev = null;
                    }else{
                        last = null;
                    }
                    //中间位置
                } else {
                    cur.prev.next = cur.next;
                    if(cur.next !=null){
                        cur.next.prev = cur.prev;
                    } else {
                        last = last.prev;
                    }
                }
                return;
            }
                cur = cur.next;
        }
    }

    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = this.head;
        while(cur != null){
            if(cur.val == key) {
                if (cur == head) {
                    head = head.next;
                    //预防只有一个节点的情况
                    if(head != null) {
                        head.prev = null;
                    }else{
                        last = null;
                    }
                    //中间位置
                } else {
                    cur.prev.next = cur.next;
                    if(cur.next !=null){
                        cur.next.prev = cur.prev;
                    } else {
                        last = last.prev;
                    }
                }
            }
            cur = cur.next;
        }
    }

    //清除链表
    public void clear(){
        while (head != null){
            ListNode curNext = head.next;
             head.next = null;
             head.prev = null;
             head = curNext;
        }
        this.last = null;
    }

}
